1. FIELD OF THE INVENTION
The present invention relates to a loudspeaker and more particularly to a loudspeaker for reproducing the highfrequency range of the audible spectrum, commonly referred to as a tweeter. The loudspeaker has a thin and relatively stiff diaphragm fixed to a driving device which forces the diaphragm to vibrate.
2. THE PRIOR ART
In the conventional types of loudspeakers for highfrequencies the diaphragm is in the form of a hollow dome of convex outer configuration and extends over almost 180.degree. spherical angle. These diaphragms of dome-shape do not focus the soundwaves emitted as do diaphragms in the form of hollow cones often used for lower sound frequencies and as those having forwardly diverging surfaces do.
In the tweeter-loudspeaker according to U.S. Pat. No. 3,059,720 the diaphragm is dome-shaped and has an annular rim or flange attached, surrounding the diaphragm. The annular flange is made of a soft material which allows the dome-shaped diaphragm to vibrate and fixes the diaphragm to a housing of the loudspeaker and centers the diaphragm at the same time. The diaphragm is rigidly fixed to a voice coil concentric therewith. The voice coil is inside an air gap of a magnetic system, the air gap surrounding the voice coil. The voice coil and the magnetic system form the driving device of the known loudspeaker. When driven by this electrodynamic driving device the diaphragm moves back and forth, whereby the annular flange is deformed. It is intended in the known type of loudspeaker, that the diaphragm moves without changing its form, i.e. oscillates as a perfectly stiff body. Nevertheless vibrations between different areas of the diaphragm cannot be avoided in practice without making the diaphragm so heavy, that its inert mass becomes too high so that the very quick motions required for high-frequency sound reproduction cannot be obtained with reasonable driving forces. Partial vibrations of areas of the diaphragm produce soundwaves not contained in the electric signal to be converted. Further the sound emission of the soft annular flange cannot be totally damped and is audible as parasitic vibrations. The annular flange, which serves to center and hold the diaphragm should be as soft as possible in order not to influence the motion of the diaphragm over the whole frequency range of the loudspeaker. In practice this aim cannot be reached at present, so that the flange thus influences the frequency response of the loudspeaker.
Tweeters should emit soundwaves in as many directions of sperical angle as possible. The angle of sound emission of the known loudspeakers having dome-shape diaphragms are smaller than 180.degree. of spherical angle. Thus a listener is always able to locate the position of the loudspeaker as the sound emission is not omnidirectional.